The present invention is generally related to radiotelephones, and more particularly to an improved cellular telephone for operating on two different cellular telephone systems.
Cellular telephones currently are designed to operate on only one type of cellular telephone system. Most countries of the world have adopted only one type of cellular telephone system. Thus, cellular telephones which operate on only one type of cellular telephone system have been adequate for the cellular systems in most countries of the world. In some countries, cellular systems have replaced and/or supplemented older non-cellular radio telephone systems. For instance, in the United States, cellular systems have replaced and/or supplemented the non-cellular, improved mobile telephone systems (IMTS) which provided radio telephone services since the late 1960s. In order to allow use of both the IMTS systems and the cellular systems, a prior art radio telephone included both an IMTS transceiver and a cellular transceiver which were coupled to a common handset control unit. In this prior art radio telephone, audio signals were switched by user selection from either the IMTS transceiver or the cellular transceiver to the common handset control unit. Use of two transceivers to provide services on two different radio telephone systems is both bulky and relatively expensive. Another type of signal switching found in prior art test equipment is mechanical bandwidth switching of the intermediate frequency (IF) section of the radio receiver in a modulation analyzer. The IF section of such test equipment was switched between two different bandwidths by diode switching circuitry in response to user activation of a mechanical switch. However, mechanical IF bandwidth switching of such test equipment is not suitable for use in cellular telephones and also requires user intervention and additional circuitry, increasing the cost and complexity thereof. For the foregoing reasons, there is a need for a cellular telephone which accommodates different receiver bandwidths for operating on different cellular telephone systems.